1. Field of the Invention
This invention relates generally to flux shields employed in dynamoelectric machines and more particularly to means for cooling such flux shields.
2. Description of the Prior Art
In operation, large dynamoelectric machines tend to produce relatively large quantities of stray flux in the end regions. This stray flux is produced by both the rotor and the end turns of the armature bars in the stator and includes axial components which tend to penetrate the end portions of the stator causing undesirable eddy current heating. It has been the practice to provide flux shields in the end regions of dynamoelectric machine stators to shield the machinery from such stray flux. An example of a flux shield is described and claimed in U.S. Pat. No. 3,714,477, Gott, assigned to applicant's assignee. The flux shield shown in the Gott patent is a copper annulus shaped to conform to an end flange. This end flange, together with an opposing end flange, clamps together a multiplicity of laminations forming the stator core to hold them in place. The flux shield being electrically conductive but having a low magnetic permeability, has circulating currents produced therein by the stray flux. These currents themselves produce a magnetic field which diverts the stray flux away from the stator core, thereby reducing undesirable eddy current losses in the end flange and other stator components. However, the currents circulating in the flux shield heat that member. Although modern dynamoelectric machines are internally cooled by a flow of cooling gas such as hydrogen, as the ratings of these machines increase with advanced technology, the heating within the flux shields employed therein may increase to an unsatisfactory level.
It is, therefore, an object of the present invention to provide an improved means for cooling the flux shields of large dynamoelectric machines without substantially increasing the fluid losses associated with the flow of cooling gas through the machines.